Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$142.42	13.613%	$161.8076	$161.81	$161.80	$161.80
Purchase #2	$130.90	12.587%	$147.3764	$147.38	$147.40	$147.40
Purchase #3	$36.29	11.324%	$40.3995	$40.40	$40.40	$40.40
Purchase #4	$173.37	13.267%	$196.371	$196.37	$196.35	$196.40
Purchase #5	$169.60	12.344%	$190.5354	$190.54	$190.55	$190.50
Purchase #6	$79.43	5.405%	$83.7232	$83.72	$83.70	$83.70
Purchase #7	$135.48	6.844%	$144.7523	$144.75	$144.75	$144.80
7 purchase totals =	$867.49		$964.9654	$964.97	$964.95	$965.00